Re: [Haskell-cafe] Pattern matching does not work like this?

No. Most constructors are functions, e.g. Just :: a -> Maybe a - a function. On the other hand, Nothing :: Maybe a is a constructor, but not a function. Andrew Wagner wrote:

Err, technically, aren't functions and constructors mutually exclusive? So if something is a function, it's, by definition, not a constructor?

On Wed, Jul 15, 2009 at 6:25 AM, Eugene Kirpichov mailto:ekirpichov@gmail.com> wrote:

Technically, the reason is not that (++) is a function, but that it is not a constructor of the [] type.

And, not only is it not a constructor, but it also *can't* be one, because the main characteristic of pattern matching in Haskell is that it is (contrary to Prolog's unification) unambiguous (unambiguity of constructors is guaranteed by the semantics of Haskell's algebraic datatypes).

If ++ could be pattern matched, what should have been the result of "let (x++y)=[1,2,3] in (x,y)"?

2009/7/15 minh thu mailto:noteed@gmail.com>: > 2009/7/15 Magicloud Magiclouds mailto:magicloud.magiclouds@gmail.com>: >> Hi, >> I do not notice this before. "fun ([0, 1] ++ xs) = .." in my code >> could not be compiled, parse error. > > ++ is a function; you can't pattern-match on that. > > Cheers, > Thu > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org mailto:Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

-- Eugene Kirpichov Web IR developer, market.yandex.ru http://market.yandex.ru _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org mailto:Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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